The use of LED light sources for lighting devices of vehicles is known, which emit light corresponding to a cosine-shaped light distribution in a half-space. Normally, a lens unit consisting of a reflector, an optical waveguide, or a lens, is mounted in front of the LED light source, in order, for example, to form a light distribution for a predefined lighting function, to generate, e.g. a blinker lighting function or a daytime running lights lighting function. The conversion into the light distribution thus occurs substantially by means of an lens unit mounted in front thereof, which must exhibit a specific structure and dimensions. By way of example, a lens unit of this type, mounted directly in front of the LED light source, is known from U.S. Pat. No. 8,475,019 B2, which is designed as a plate-shaped optical waveguide. The efficiency of the lens unit is substantially determined by how much light of the light source can be used. With a cosine-shaped light distribution of the light source and small light surfaces of the lens unit, such as a narrow light entry surface of an optical waveguide, significant light portions of the light source, which are emitted at lateral angles, cannot be acquired and used.